1. Field of the Invention
The present invention relates to a process for modifying the surface of an inorganic biomaterial and more particularly to a process for modifying the surface of an inorganic biomaterial which is useful as an implant material for artificial bones, dental implants, etc., to further improve the bioactivity of the biomaterial.
2. Description of Prior Art
As so-called bioactive ceramics capable of forming a chemical bonding with bones, there are known sintered apatite and a crystallized glass in the system of Na.sub.2 O-K.sub.2 O-MgO-CaO-SiO.sub.2 -P.sub.2 O.sub.5. As the bioactive ceramic, there is further known a crystallized glass in the system of MgO-CaO-P.sub.2 O.sub.5 -SiO.sub.2. This crystallized glass contains an apatite crystal and a wollastonite crystal, and the apatite crystal contributes to the bioactivity and the wollastonite crystal contributes to the mechanical strength. As to the bending strengths of these ceramics, the sintered apatite has about 1,000 to 1,400 kg/cm.sup.2 ; the Na.sub.2 O-K.sub.2 O-MgO-CaO-SiO.sub.2 -P.sub.2 O.sub.5 system crystallized glass about 1,000 to 1,500 kg/cm.sup.2 ; the MgO-CaO-P.sub.2 O.sub.5 -SiO.sub.2 system crystallized glass about 1,200 to 1,400 kg/cm.sup.2.
A CaO-P.sub.2 O.sub.5 -SiO.sub.2 system or CaO-P.sub.2 O.sub.5 -SiO.sub.2 -(MgO, Y.sub.2 O.sub.3) system crystallized glass containing a larger amount of a wollastonite crystal is also known, and it has a high bending strength of 1,700 to 2,300 kg/cm.sup.2.
However, these bending strengths are not yet fully satisfactory from the standpoint that the above materials are used as an artificial bone or a dental implant. Hence, a biomaterial of higher strength is desired.
As biomaterials of higher strength, there are known composite sintered products consisting of a bioactive crystallized glass as mentioned above and a high strength ceramic powder (e.g. zirconia, alumina, or zirconia-alumina). These composites have a high bending strength of 2,500-3,800 kg/cm.sup.2 which is comparable to that of sintered alumina.
The above ceramic-crystallized glass composites, however, have lower bioactivity to bones than crystallized glasses per se because in the composites the content of the crystallized glass capable of forming a chemical bonding with bones is reduced by the incorporation of the ceramic incapable of forming a chemical bonding with bones by itself. Therefore, it is desired to improve the bioactivity of the composites.
Crystallized glasses per se have poor bioactivity in some cases, depending upon their compositions. Therefore, it is also desired to improve the bioactivity of crystallized glasses having low bioactivity.
Hence, an object of the present invention is to improve a process for modifying the surface of an inorganic biomaterial such as a crystallized glass or a ceramic-crystallized glass composite in order to improve its bioactivity.
Other objects of the present invention will be apparent from the following descriptions and drawings.